I've used tool batteries (Makita) in series for many years to power my ebike builds. The latest generation of genuine Makita batteries have a true BMS that cuts discharge if any cell drops below 3V. Makita only makes 10 cell 18V batteries (6ah max) and they are rightfully expensive. There are 15 cell and and now 20 cell cases filled in China with cell of various quality. They still use old style charge boards inside without any individual cell monitoring or protection.
I have batteries built to order with EV quality high capacity cells and have had no battery problems even operating without a true BMS. But I do the math ahead to be sure I won't run out of AH/Wh and allow a decent saftey margin. I often scan the cell voltages before after rides to be sure cells are balanced. Others with the same batteries ride until the bike stops working (controller LVC) which often ruins cells.
5S 20A BMS boards are now available (~$2) that fit inside Makita clone batteries (with some adjustments). The batteries still mount on standard makita 18V tools but have to be charged with a simple 21V, 2 wire charger. I tested 1 today. Charging seemed to be have decent balancing. Discharge however is a concern. I assumed BMS would cut off the battery if any cell went below 3V. It did not; not even 2.8V. I finally found the specs and it say discharge protection voltage 2-2.8V/cell. My question: does that cutoff give any significant damage protection the weaker cells?
I have batteries built to order with EV quality high capacity cells and have had no battery problems even operating without a true BMS. But I do the math ahead to be sure I won't run out of AH/Wh and allow a decent saftey margin. I often scan the cell voltages before after rides to be sure cells are balanced. Others with the same batteries ride until the bike stops working (controller LVC) which often ruins cells.
5S 20A BMS boards are now available (~$2) that fit inside Makita clone batteries (with some adjustments). The batteries still mount on standard makita 18V tools but have to be charged with a simple 21V, 2 wire charger. I tested 1 today. Charging seemed to be have decent balancing. Discharge however is a concern. I assumed BMS would cut off the battery if any cell went below 3V. It did not; not even 2.8V. I finally found the specs and it say discharge protection voltage 2-2.8V/cell. My question: does that cutoff give any significant damage protection the weaker cells?
